In recent years, low-power display units (displays) with high image quality have been in increasing demand, as mobile devices represented by mobile phones and portable information terminals have become widespread. In particular, distribution service of digital books has recently started, and a display having a display quality suitable for reading is desired.
Although displays such as a cholesteric liquid crystal display, an electrophoretic display, an electric-redox-type display, and a twisting ball display have been proposed as such displays, a reflection-type display is advantageous for reading. In the reflection-type display, bright display is performed with use of reflection (scattering) of external light in a manner similar to that of a paper and thus, display quality close to that of the paper is achieved.
Among the reflection-type displays, an electrophoretic display using electrophoresis phenomenon that is low in power consumption and high in response speed is expected to be a major display. As the display method, the following two methods have been mainly proposed.
In a first method, two kinds of charged particles are dispersed in an insulating liquid, and the charged particles are moved in response to an electric field. The two kinds of charged particles are different in optical reflection characteristics from each other, and its polarities are opposite to each other. In this method, a distribution state of the charged particles is changed in response to the electric field, and an image is displayed.
In a second method, charged particles are dispersed in an insulating liquid, and a porous layer is disposed (for example, PTL 1). In this method, the charged particles move through pores of the porous layer in response to the electric field. For example, the porous layer may include a fibrous structure formed of a polymer material and non-migrating particles held by the fibrous structure. For example, polyacrylonitrile having a cyano group high in polarity may be used for the fibrous structure.